IE1 = (VCC – VCE) / (R1 + R2 + R3)
= 12v – 0v / 20k + 2k + 8k
= 12v / 30k
= 0.4mA
Let assume VCE Q1 = 6.0v
IE1 = (VCC – VCE) / (R1 + R2 + R3)
= 12v – 6v / 20k + 2k + 8k
= 6v / 30k
= 0.2mA
VE Q1 = IE1 x (R2+R3)
= 0.2mA x 10k
= 2v
VB Q1 = VE1 + VBE1
= 2v + 0.7v
= 2.7v
VB Q2 = VCC – (R1 x IE1)
= 12v – 4v
= 8v
VE Q2 = VB Q2 – VBE Q2
= 8v – 0.7v
=7.3v
VR5 = ½ x VE Q2
= 3.65v
*VR5 should be near to VB Q1 = 2.7v, this show IE1 is too low, we need to increase it. Try IE1 = 0.3mA
VE Q1 = IE1 x (R2+R3)
= 0.3mA x 10k
= 3v
VB Q1 = VE1 + VBE1
= 3v + 0.7v
= 3.7v
VB Q2 = VCC – (R1 x IE1)
= 12v – 6v
= 6v
VE Q2 = VB Q2 – VBE Q2
= 6v – 0.7v
=5.3v
VR5 = ½ x VE Q2
= 2.65v
*VR5 should be near to VB Q1 = 2.7v, this show equal to VB Q1 to low. Try with IE1 = 0.25mA
VE Q1 = IE1 x (R2+R3)
= 0.25mA x 10k
= 2.5v
VB Q1 = VE1 + VBE1
= 2.5v + 0.7v
= 3.2v
VB Q2 = VCC – (R1 x IE1)
= 12v – 5v
= 7v
VE Q2 = VB Q2 – VBE Q2
= 7v – 0.7v
=6.3v
VR5 = ½ x VE Q2
= 3.15v
*This result is close for VB Q1.
Let IE1 = 0.24mA
VE Q1 = IE1 x (R2+R3)
= 0.24mA x 10k
= 2.4v
VB Q1 = VE Q1 + VBE Q1
= 2.4v + 0.7v
= 3.1v
VC Q1 = VCC – (IE1 x R1)
= 12v – 4.8v
= 7.2v
VB Q2 = VC Q1
= 7.2v
VE Q3 = VB Q2 – VBE Q2
= 7.2v – 0.7v
= 6.5v
IE2 = VE Q2 / (R4 + R5)
= 6.3v / 2k
= 3.15mA
So: IE1 = 0.25mA and IE2 = 3.15mA.
re1 = VT / IE1
= 26mV / 0.25mA
= 104 Ohm.
re2 = VT / IE2
= 26mV / 3.15 mA
= 8.25 Ohm.
IB1 = IE1 / Beta
= 0.25mA / 100
= 0.0025mA
IC1 = 1+Beta x IB1
= 101 x 0.0025
= 0.253mA
Av1 = IC1xRC / IE1 x re1
= 0.253mA x 20k / 0.25mA x 104 Ohm
= 5.06v / 26mV
= 0.19 v
Av2 = 12v / IE2 x re2
= 12v / 3.15mA x 8.25 Ohm
= 12v / 25.99mV
= 0.462 v